Combination reactor system

ABSTRACT

The present invention is directed to a combination reactor system for exothermic reactions comprising a trickle-bed reactor and a shell-and-tube reactor. This combination allows the system to efficiently remove heat while also providing the ability to control both the temperature and/or reaction progression. The trickle-bed reactor removes heat efficiently from the system by utilizing latent heat and does not require the use of a cooling or heating medium. The shell-and-tube reactor is used to further progress the reaction and provides a heat exchanger in order to introduce fluid at the desired temperature in the shell-and-tube reactor. Also, additional reactant or reactants and/or other fluids may be introduced to the shell-and-tube section of the reactor under controlled temperature conditions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional filing from commonly owned U.S. patentapplication Ser. No. 13/245,328, filed Sep. 26, 2011, now U.S. Pat. No.8,969,634, the disclosure of which is hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

With the highly exothermic nature of some reactions, including thehydrogenation of certain fluorocarbons, there is a need to remove heatwhile a reaction progresses. Traditional shell-and-tube reactors oftendo not have enough heat transfer ability to keep the reaction systems atreasonable operating conditions. On the other hand, a purely trickle-bedreactor setup does not always provide enough ability to control both thetemperature and/or reaction progression.

Generally, a shell-and-tube catalytic reactor is a type of reactor whichis used to efficiently add or remove reaction heat. In some uses ofthese reactors, a catalyst is filled in a plurality of reaction tubes; areaction fluid (gas and/or liquid) into the reaction tubes to cause achemical reaction for obtaining a desired product; and a heat transfermedium is circulated through the reactor shell such that the chemicalreaction can occur under controlled thermal conditions.

Shell and tube reactors typically include a number of reaction tubesheld in place in the shell by one or more tubesheets; shell nozzles areused for introducing and withdrawing the heat transfer medium; tubenozzles are used for introduction of reactants into the reaction tubesand for withdrawing product therefrom; and appropriate dividers and/orbaffles are used to separate the respective reactor parts for theirspecific functions. The reactor parts are typically made from materialsthat do not react with the materials being processed in the reactor.

The term trickle bed reactor is used to describe a reactor in which aliquid phase and a gas phase flow concurrently downward through a fixedbed of catalyst particles while reaction takes place. At sufficientlylow liquid and gas flow rates the liquid trickles over the packing inessentially a laminar film or in rivulets, and the gas flowscontinuously through the voids in the bed.

A useful general review of trickle bed reactors and other multiphasereactors can be found under the heading “Reactor Technology” in“Kirk-Othmer Encyclopedia of Chemical Technology”, Third Edition, Volume19, at pages 880 to 914. This reference states the following at page892, “Trickle-bed reactors have complicated and as yet poorly definedfluid dynamic characteristics. Contacting between the catalyst and thedispersed liquid film and the film's resistance to gas transport intothe catalyst, particularly with vapor generation within the catalyst, isnot a simple function of liquid and gas velocities.”

In operation, a typical trickle bed reactor has a fixed catalyst bedpositioned vertically. A reaction mixture comprising a liquid, a gas orboth, flows downwardly through the bed. The exothermic heat of reactionis absorbed by vaporizing a combination of reactant, product,by-product, and optionally solvent. For a reaction to occur, thereactants must diffuse into the liquid phase, then diffuse to thecatalyst particles, and then react. The reaction products, if soluble inthe liquid phase, are then removed from the reactor.

The total reaction mechanism in such a system thus includes the steps ofdiffusion and reaction. The reactants must diffuse into the liquid phaseand then diffuse to the catalyst particles, and the reaction rate isthus affected by the rate of diffusion to the catalyst particles.Assuming a situation where the catalytic reaction occurs at the surfaceof the catalyst particles, the reaction rate is affected further by thereaction rate constant, the concentration of the reactants at theparticle surface, and the surface area of the catalyst particles. Theresulting reaction products must then diffuse away from the catalystparticles and back to the mainstream liquid flow. Accordingly, the finalreaction rate, as controlled by the slowest of the aforementioned steps,and is affected most by either the rate at which catalysis proceeds orthe rate at which diffusion of the reactants and the products proceeds.The primary resistance to diffusion occurs at boundary layer areas, andthus it would be advantageous to increase both the gas and the liquidflow rates to decrease such boundary layers.

PRIOR ART

The following prior art documents are hereby incorporated herein byreference in their entirety.

U.S. Pat. No. 3,566,961 is entitled “tubular reactor for carrying outendothermic and exothermic reactions with forced circulation.” Thispatent teaches a tubular reactor with forced circulation of a heattransfer medium which flushes the outside of the reaction tubes in axialdirection, the heat transfer medium being supplied to, and withdrawnfrom, the reactor wall uniformly through circular pipelines, andparticularly the constructional shape of deflecting guide plate meansarranged transversely to the direction of flow and having annularopenings around the reaction tubes for uniform flow towards all thetubes of the nest of tubes.

U.S. Pat. No. 3,792,980 is entitled “reactor for carrying out reactionsaccompanied by a change in heat.” This patent teaches a shell and tubereactor for reactions accompanied by a change in heat. Reaction materialflows through the tubes and a heat exchange medium flow through theshell to remove or supply heat of the reaction. Also a pump disposed inthe reactor on the shell side circulates the heat exchange medium withinthe shell. The tubes are disposed in spaced sectors so that passagewaysare provided for the circulating heat exchange medium. Heat exchangemedium is withdrawn and supplied to the shell and is itself subjected toheat exchange outside the reactor. Improved distribution of the heatexchange medium within the shell is obtained by withdrawing andsupplying the heat exchange medium, respectively, from and to theaforesaid passageways.

U.S. Pat. No. 4,101,287 is entitled “combined heat exchanger reactor.”This patent teaches a one-piece, integral, high strength, combined heatexchanger-reactor comprising a monolithic honeycomb structure whereinthe channels thereof are divided into two or more groups; group onecarrying one fluid and group two carrying another fluid which differsfrom the first in composition and/or temperature and/or pressure and/ordirection of flow, the main design feature of the combined heatexchanger-reactor (CHER) being that group one channels extend outwardparallel to the channel axis and perpendicular to the cross-section ofthe honeycomb and each channel of this group one being in thermalcontact through common walls with channels of group two while eachchannel of group one is separated from other channels of group one bythe intervening voids formed by the presence of the channels of grouptwo.

U.S. Pat. No. 4,929,798 is entitled “pseudoadiabatic reactor forexothermal catalytic conversions.” This patent teaches a multitubularcatalytic reactor for exothermal catalytic reactions comprises a bundleof parallel tubes all of the same length and a catalyst within thetubes. The tube bundle has an inlet side and an outlet side. Devices areprovided for introducing separately reactants to within the tubes of thereactor and coolant to the channels defined between adjacent tubes ofthe bundle. The coolant is introduced into the channels co-currentlywith the direction of flow of the reactants. The products are withdrawnfrom the tubes independently of the coolant.

U.S. Pat. No. 5,027,891 is entitled “method for transferring heatbetween process liquor streams.” This patent teaches a method oftransferring heat between process liquor streams such as streams ofcaustic liquor in the Bayer process for producing alumina from bauxite,utilizing a heat pipe arrangement for heat exchange. The process streamsrespectively pass in contact with one surface of a first heat-exchangewall and one surface of a second heat-exchange wall while being isolatedfrom the second surfaces of the two walls; these second walls areexposed to a closed volume (also isolated from both process streams)containing a heat transfer fluid that vaporizes below the temperature ofthe hotter process stream and condenses above the temperature of thecooler process stream. The heat transfer fluid vaporizes at the exposedsurface of the wall contacted by the hotter stream, and condenses at theexposed surface of the wall contacted by the cooler stream, therebytransferring heat (as heat of vaporization) from the former stream tothe latter.

U.S. Pat. No. 6,180,846 is entitled “process and apparatus using platearrangement for combustive reactant heating.” This patent teaches aprocess and apparatus for indirectly heating an endothermic reaction bycombustion of reactants or products from the endothermic reaction usinga plate heat exchange arrangement in a highly efficient manner. Thisinvention is particularly suited for processes such as the production ofstyrene or synthesis gas.

U.S. Pat. No. 6,790,431 is entitled “reactor for temperaturemoderation.” This patent teaches embodiments which include methods andapparatus for arranging multiple reaction zones such that at least onehot spot in one of the reaction zones is moderated by a cooler spot inan adjacent reaction zone.

U.S. Pat. No. 7,521,028 is entitled “catalytic reactor for low-Btufuels.” This patent teaches an improved catalytic reactor which includesa housing having a plate positioned therein defining a first zone and asecond zone, and a plurality of conduits fabricated from a heatconducting material and adapted for conducting a fluid therethrough.

SUMMARY OF THE INVENTION

The present invention is directed to a combination reactor system forexothermic reactions comprising a trickle-bed reactor and ashell-and-tube reactor. This combination allows the system toefficiently remove heat while also providing the ability to control boththe temperature and/or reaction progression. The trickle-bed reactorremoves heat efficiently from the system by utilizing latent heat anddoes not require the use of a cooling or heating medium. Theshell-and-tube reactor is used to further progress the reaction andprovides a heat exchanger in order to introduce fluid at the desiredtemperature in the shell-and-tube reactor. Also, additional reactant orreactants and/or other fluids may be introduced to the shell-and-tubesection of the reactor under controlled temperature conditions.

These reactors can be separated by a heat exchanger in order tointroduce fluid at the desired temperature to the shell-and-tubereactor. Also, additional reactant or reactants and/or other fluids maybe introduced to the shell-and-tube section of the reactor.

The trickle-bed and shell-and-tube or trickle-bed, heat exchanger, andshell-and-tube setup can be connected in a way so as to provide theoptimal system for reaction progress and heat exchange as required byany process. For instance, the pieces of equipment could be stacked withthe trickle-bed reactor on top and shell-and-tube reactor on the bottom.This saves floor space.

The trickle-bed reactor would be similar to the trickle-bed normallyused in chemical engineering with a fixed bed or reactor catalyst andtwo phases present in the reactor.

The shell-and-tube reactor could be a multi-stage, multi-tube,shell-and-tube heat exchanger which contains reactor catalyst in certaintubes and optionally, no catalyst in other tubes. See, for example, U.S.Patent Pub. Nos. 2011-0054226 and 2010-0307726, the disclosures of whichare hereby incorporated herein by reference.

If desired, a simpler shell-and-tube reactor design could be provideddepending on the systems requirements. The heat exchanger could be atraditional heat exchanger used for removing or adding heat or causing aphase change of the process fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of the combination reactor system ofthe present invention, showing a combined trickle bed reactor and ashell and tube reactor system.

FIG. 2 illustrates one embodiment of a trickle bed reactor useful in thecombination reactor system of the present invention.

FIG. 3 illustrates one embodiment of a shell and tube reactor useful inthe combination reactor system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As described above, the present invention is directed to a combinationreactor system comprising a trickle-bed reactor connected to ashell-and-tube reactor. This reactor combination is especially usefulfor conducting exothermic reactions, i.e., reactions that areaccompanied by the evolution of heat as the reaction occurs. Highlyexothermic reactions, i.e., reactions that produce high temperatures canbe safely conducted in the combination reactor system of the presentinvention. Typically, hydrogenation, oxidation and chlorination arerecognized as highly exothermic reactions.

This system allows the reaction operators to efficiently add and/orremove heat from the reaction system while also providing the ability tocontrol both the temperature and/or reaction progression. Thetrickle-bed reactor removes heat efficiently from the system byutilizing latent heat and does not require a cooling or heating medium.The shell-and-tube reactor is used to further progress the reaction andto provide rapid heat exchange ability should the reaction progress notbe meeting desired requirements.

As illustrated in FIGS. 1, 2 and 3, the combination reactor system ofthe present invention comprises a trickle-bed reactor followed by ashell-and-tube reactor. This system allows highly exothermic reactionsto precede under the precise control of the system operators, as thecombined reactor system allows for the efficient addition and/or removalof heat from the reaction, while also providing the ability to controlboth the temperature and/or reaction progression.

FIG. 1 illustrates one embodiment of a combination reactor system of thepresent invention, comprising a trickle-bed reactor 100 mounted to ashell-and-tube reactor 300. As shown therein, the upper reactor is thetrickle bed reactor 100. This reactor includes a reactant inlet nozzle110 and a relief nozzle 120 at the top part of the reactor. Internally,this reactor includes an inlet baffle 130 and an inlet distributor 140.Also shown are the catalyst fill nozzle 150, a thermowell 160, acatalyst removal nozzle 170, and a catalyst support grid 180.

A liquid collector tray 190, is placed between the between the tworeactor sections. Gas will continue to flow down to the shell & tubereactor, whereas liquid product may be optionally withdrawn from thesystem via liquid drawoff nozzle 200. Should any additional reactants berequired at this stage of the processing, they may be added viaintermediate feed nozzle 210.

As further illustrated in FIG. 1, the bottom portion of the combinationreactor system of the present invention includes the shell and tubereactor 300. This reactor includes an upper shell nozzle 310 and a lowershell nozzle 320. One of the multiple reactor tubes 330 is shown in thereactor, and each tube includes a tube cover 340. The tubes arepositioned in the reactor with a baffle 350. The reactor outlet nozzle360 is shown at the bottom.

The trickle-bed removes reaction heat efficiently from the system byutilizing latent heat and does not require a cooling or heating medium.One embodiment of such a reactor is shown in FIG. 2. As shown therein,the reactor includes a bed of catalyst, and various inlet and outletports, baffles and distributors for conducting reactions therein.

As illustrated in FIG. 2, the reactor includes the following components;

-   -   A1—reactant inlet nozzle    -   V1—relief nozzle    -   N1—catalyst fill nozzle    -   T1—thermowell    -   N2—catalyst (HK) outlet nozzle    -   B1—reactor outlet nozzle

The shell-and-tube reactor is used to further progress the reaction andto provide heat exchange ability should the reaction progress past thedesired process design. One embodiment of such a reactor is shown inFIG. 3. As shown therein, the reactor includes tubes of supportedcatalyst, and various inlet and outlet ports, baffles and distributorsfor conducting reactions therein.

As illustrated in FIG. 3, the reactor includes the following;

-   -   10—Tube nozzle    -   12—Divider    -   14—Baffle Plate    -   16—Head    -   18—Tube    -   20—Tube cover    -   22—Catalyst support    -   24—Tubesheet    -   26—Shell    -   28—Shell nozzle    -   30—Baffle    -   32—Support lug

As described above, if desired these reactors can be separated by a heatexchanger in order to introduce fluid at the desired temperature to theshell-and-tube reactor.

If desired, additional reactant or reactants and/or other fluids may beintroduced to the shell-and-tube section of the reactor.

The trickle-bed and shell-and-tube or trickle-bed, heat exchanger, andshell-and-tube setup can be done in a way so as to provide the optimalsystem for reaction progress and heat exchange as required by anyprocess.

In one embodiment, the pieces of equipment are stacked with thetrickle-bed reactor on top and shell-and-tube reactor on the bottom;thereby preserving floor space. Here, the trickle bed reactor is similarto the trickle-bed normally used in chemical engineering with a fixedbed of reactor catalyst and two phases in the reactor. Theshell-and-tube reactor is a multi-stage, multi-tube, multi-heating zone,shell-and-tube heat exchanger which contains reactor catalyst in certaintubes and optionally, no catalyst in other tubes. See U.S. Patent Pub.No. 2010-0307726 A1. For another preferred design, see U.S. Patent Pub.No. 2011-0054226 A1.

However, a simpler shell-and-tube reactor design could be used,depending on the reaction and/or systems requirements. The heatexchanger could be a traditional heat exchanger used for removing oradding heat or causing a phase change of the process fluid. Even in thecase of a traditional shell & tube reactor, some or all of the tubes maybe filled with catalyst.

As described above, the present invention is preferably designed for usewith exothermic reactions. For example, reactions involving thecatalytic hydrogenation of fluoro-olefins are typically exothermic, andthese reactions are one preferred type of reaction that may be conductedin the combination reactor of the present invention. In such a case thereactor should be constructed from materials which are resistant to thecorrosive effects of the reagents employed therein. Typical materialsfor the reactors include metals such as nickel and its alloys, includingHastelloy, Inconel, Incoloy, and Monel or vessels lined withfluoropolymers. Other suitable materials used under suitable conditionscould be steel or stainless steel.

The process flow may either be in the down or up direction through a bedof the catalyst in the shell and tube reaction zones. If the reactionzones require heating for optimal reaction, one or more of thetemperature control zones is charged with a heating medium that providessufficient heat to the reaction zones to provide the desired reactiontemperature. Materials suitable for use as a heating medium are wellknown to persons having ordinary skill in this art, and include forexample, hot tempered water, hot oil, and condensing steam. Similarly,if the reaction zones require cooling to maintain optimal reactionconditions, one or more of the temperature control zones is charged witha suitable cooling medium that removes heat and achieves or maintainsthe desired temperature in the reaction zones. Materials suitable foruse as a cooling medium are well known to persons having ordinary skillin this art, and include for example, cooling water and boiling water.

In commercial processes where a fluoro-olefin C_((n))H_((2n-x))F_((x))to C_((n))H_((2n−x+2))F_((x)) is hydrogenated (e.g., hexafluoropropyleneto 236ea, 1225ye to 245eb, and the like), inadequate management orcontrol of heat removal may induce excess hydrogenation, decompositionand hot spots resulting in reduced yields and potential safety issues.In the hydrogenation of fluoro-olefins, it is therefore necessary tocontrol the reaction temperature as precisely as practical to overcomechallenges associated with heat management and safety.

REACTION EXAMPLES

Particularly useful reactions to make use of this invention include thefollowing:Hexafluoropropylene+H₂→1,1,1,2,3,3-hexafluoropropane(HFC-236ea);  Reaction(1)and1,2,3,3,3-pentafluorpropene (HFC-1225ye)+H₂→1,1,1,2,3-pentafluoropropane(HFC-245eb).  Reaction (2)

Note, an undesired over-hydrogenation product in Reaction (2) is1,1,1,2-tetrafluoro-propane (HFC-254eb).

As used herein, the singular forms “a”, “an” and “the” include pluralunless the context clearly dictates otherwise. Moreover, when an amount,concentration, or other value or parameter is given as either a range,preferred range, or a list of upper preferable values and lowerpreferable values, this is to be understood as specifically disclosingall ranges formed from any pair of any upper range limit or preferredvalue and any lower range limit or preferred value, regardless ofwhether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily appreciatedby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. It is intended that the claims be interpreted to coverthe disclosed embodiment, those alternatives which have been discussedabove and all equivalents thereto.

What is claimed is:
 1. A reactor system for use with an exothermicreaction comprising the hydrogenation of a fluoro-olefin compound, saidsystem comprising in combination, (a) as a first reactor in the system,a trickle-bed reactor which does not include either a heating or coolingmedium, and (b) as a second reactor in the system, a shell-and-tubereactor which comprises a temperature control system selected from thegroup consisting of a heating medium, a cooling medium, and both aheating and a cooling medium, wherein the reactors are separated by aheat exchanger; wherein the trickle bed reactor comprises a fixed bed ofreactor catalyst and two phases in the reactor; wherein theshell-and-tube reactor comprises a multi-stage, multi-tube,shell-and-tube heat exchanger which contains reactor catalyst in alltubes; and wherein the reactor system provides for the removal of heatand provides the ability to control reaction temperature and/or reactionprogression.
 2. The combination reactor system of claim 1, wherein theheat exchanger is used for removing or adding heat or causing a phasechange of a reaction medium.
 3. The combination reactor system of claim1, wherein the trickle-bed reactor removes heat from the system byutilizing latent heat.
 4. The reactor system of claim 1, wherein thehydrogenation reaction is the conversion of hexafluoropropylene to1,1,1,2,3,3-hexafluoropropane.
 5. The reactor system of claim 1, whereinthe hydrogenation reaction is the conversion of1,2,3,3,3-pentafluoropropene to 1,1,1,2,3-pentafluoropropane.
 6. Acombination reactor system for use with an exothermic reactioncomprising the hydrogenation of a fluoro-olefin compound, said systemcomprising in combination, (a) a trickle-bed reactor as the firstreactor in the system; and (b) a shell-and-tube reactor as the secondreactor in the system; wherein the trickle-bed reactor removes heat fromthe system by utilizing latent heat and does not require the use of acooling or heating medium; wherein the shell-and-tube reactor comprisesa shell structure and a tubesheet located in the shell structure;wherein the tubesheet comprises one or more reaction zones and one ormore temperature control zones, wherein each reaction zone comprises aplurality of aligned reaction tubes; and each temperature control zonecomprises a plurality of aligned temperature control tubes; wherein thereactor system further comprises a heat exchanger in order to introducematerials to the reactors at predetermined temperatures, therebycontrolling the reaction conditions in the combination reactor system;and wherein each reaction zone of the shell-and-tube reactor is adjacentto a temperature control zone.
 7. The reactor system of claim 6, whereinthe hydrogenation reaction is the conversion of hexafluoropropylene to1,1,1,2,3,3-hexafluoropropane.
 8. The reactor system of claim 6, whereinthe hydrogenation reaction is the conversion of1,2,3,3,3-pentafluoropropene to 1,1,1,2,3-pentafluoropropane.